Recovery of hydrocarbons by in situ combustion



United States Patent [72] Inventor Dixon W. Peacock Bartlesville, Oklahoma [21 j Appl. No. 770,249 [22] Filed Oct. 24, 1968 [45] Patented Dec. 8, 1970 [73] Assignee Phillips Petroleum Company a corporation of Delaware 54] RECOVERY OF HYDROCARBONS BY IN SlTU COMBUSTION 9 Claims, 2 Drawing Figs.

[52] U.S. Cl. 166/256 [51] E21b43/24 [50] Field of Search 166/256, 260, 261, 251, 263, 272

[56] References Cited UNITED STATES PATENTS 2,793,696 5/1957 Morse 166/256 3,110,345 11/1963 Reed et al 166/261 3,111,986 11/1963 Kuhn, Jr 166/256 3,126,955 3/1964 Trantham et a1. 166/256 3,127,935 4/1964 Poettmann et al.... 166/260 3,135,324 6/1964 Marx 166/261X 3,154,143 10/1964 Parrish 166/256 3,174,544 3/1965 Campion et al.... 166/256 3,221,812 12/1965 Prats 166/261 3,386,507 6/1968 Lumpkin 166/256 Primary Examiner-Stephen J. Novosad Attorney-Young and Quigg ABSTRACT: An in situ combustion process for recovery of hydrocarbons wherein in a first stage of the process hydrocarbons are produced from an underground formation by countercurrent drive in situ combustion and in a second stage of the process hydrocarbons are produced from said formation by direct drive in situ combustion. Said direct drive in situ combustion is deliberately initiated prior to completion of said countercurrent in situ combustion.

PRODUCT PATENATEDHEB 8l970 4 3545544 AIR? AIR |8 PRODUCT INVENTOR.

D. W. PEACOCK A T TORNE VS RECOVERY OF HYDROCARBONS BY IN SI'I'U COMBUSTION This invention relates to the recovery of hydrocarbons by in situ combustion.

In situ combustion in the recovery of hydrocarbons from underground strata containing carbonaceous material is becoming more prevalentin the petroleum industry. In this technique of production, combustion is initiated in a carbonaceous formation and the resulting combustion zone is caused to move through the formation by either direct or countercurrent drive whereby the heat of combustion of a portion of the hydrocarbon in the formation drives out and frequently upgrades a substantial proportion of the unburned hydrocarbon material.

. Typically, an arrangement for carrying out an in situ combustion process can include an input or injection well for the introduction of an oxygen containing gas, such as air, into the formation and an output or-production well for the removal of products from the formation. Indirect drive process an oxygen-containing gas is introduced into the formation through the injection well and a combustion front is initiated in the formation around said injection well. Direct drive processes have the advantage of being relatively. simple to carry out. Another advantage of direct drive processes is that comparatively less hydrocarbons are burned than in countercurrent drive processes. A disadvantage of direct drive processes, particularly when used in formations containing very viscous hydrocarbons, is thatthere sometimes is a buildup of a relatively immobile bank of viscous liquid hydrocarbons in the formation downstream from the combustion front. This bank of liquid hydrocarbons tends to block the formation and thus impede, or restrict completely, the flow of combustion-sup porting gases from the input well through the formation to the production well. When this happens, the combustion front frequently dies out. w

i In order to overcome this disadvantage the countercurrent flow or reverse flow combustion process has been developed. In a countercurrent flow process combustion is initiated at the output or production well by heating the formation and injecting an oxygen-containing gas, such as air, into the heated area. Initially, the oxygen-containing gas can be injected through either the injection well or the production well. However, after the combustion front is established introduction of the oxygen-containing gas through the production well is terminated and is then introduced only through the injection well. This causes the combustion front to move through the formation in a direction away from the production well and toward the injection well.

A serious disadvantage of countercurrent in situ cornbustion processes is the problem of spontaneous or autoignition which will take place in portions of the formation upstream from the advancing combustion front. Said autoignition results from the slowox-idation of the crude oil or other organic matter in the formation by the oxygen-containing gas as it flows through said formation from the injection well to the combustion front and production well. Said slow oxidation generates oxygen-containingwhich increases the temperature of the formation to the point where eventually autoignition or spontaneous ignition occurs. When this occurs it is difficult to control. Furthermore, there is usually little or no oxygen left to support the desired counterflow combustion front and, as a result, this latter front dies out.

The present invention provides an improved in situ combustion process which combines the advantages of both direct drive and countercurrent drive processes and eliminates, or at least mitigates, the disadvantages of said direct and countercurrent processes. Broadly speaking, the present invention comprises an in situ combustion process wherein in a first stage of the process hydrocarbons are produced from the formation by countercurrerit drive in situ combustion and in a second stage of the process hydrocarbons are produced from said formation by directdrive in situ combustion.

An object of this invention is to provide an improved in situ combustion process. Another object of this invention is to provide an improved in situ combustion process wherein the ad vantages of both direct drive and countercurrent drive are realized. Another object of this invention is to provide an improved in situ combustion process wherein the disadvantages of direct drive and countercurrent drive are eliminated, or at least mitigated. Another object of this invention is to provide an improved in situ combustion process which is particularly adapted for producing hydrocarbons from formations containing heavy viscous crudeoils. Other aspects, objects, and advantages of the invention will be apparent to those skilled in the art in view of this disclosure.

Thus, according to the invention, there is provided a process for producing hydrocarbons from a permeable oilbearing subterranean formation penetrated by at least one injection well and at least: one production well, which process comprises, in combination, the steps of: (a) injecting a stream of oxygen-containing gas through one of said wells into said formation; (b) initiating a first combustion front in said formation at said production well; (c) terminating any injection of oxygen-containing gas through said production well; (d) maintaining said first combustion front by injection of oxygen-containing gas through said injection well at a rate and for a period of time sufficient to cause said first combustion front to move out into said formation in a direction away from said production well and toward said injection well by counterflow in situ combustion for a substantial distance, but insufficient for autoignition to occur in saidforrnation between said injection well and said first combustion front; (e) thereafter, igniting a second combustion front in said formation at said injection well;(f) permitting said first combustion front to die out from lack of oxygen due to essentially all of the oxygen in said oxygen-containing gas being consumed in said second com bustion front; (g) continuing injection of said oxygen-containing gas through said injection well to move said second combustion front through said formation toward said production well by direct drive in situ combustion; (h) driving hydrocarbons in said fon'nation through the area of said stratum traversed by said first combustion front and to said production well; and (i) recovering hydrocarbons from said production well.

The invention is applicable to the recovery of hydrocarbons from any type of permeable formation containing same. The invention is particularly applicable to the recovery of hydrocarbons from formations containing crude oils. A particularly valuable application of the invention resides in the recovery of hydrocarbons from formations containing heavy tars and/or viscous crude oils having; and API gravity of not more than about 10 to 12.

FIG. 1 is a diagrammatic illustration of a first stage of the process of the invention in progress.

FIG. 2 is a diagrammatic illustration of a second stage of the process of the invention in progress.

Referring now to the drawings, wherein like reference numerals are employed to denote like elements, the invention will be more fully explained. It will be understood that said drawings are diagrammatic and many valves, pumps, control equipment, and other elements not necessary for explanation of the invention have been ommitted for brevity. In FIG. 1 a first well 10, here referred to as an injection well, extends from the surface of the earth into a porous subterranean formation 12 which it is desired to produce. Conduit means 14 is provided for introducing air or other oxygen-containing gas into said formation 12 through said injection well 10. Said conduit means 14 can comprise any conventional means for supplying and introducing an oxygen-containing gas into an underground formation. A second well 16, here referred to as a production well, is spaced apart from said first well and also extends from the surface of the earth into said formation 3.2;. Conduit means 18 is provided for introducing air or other oxygen-containing gas into said well 16, if desired. conduit means 20 is provided for removing produced hydrocarbons and other products of the process from said formation via said well 16. While conduits l8 and 20 are shown as employing a common connection header to said well 16, it will be understood that said conduits can be separately connected to either the tubing or the annular space around the tubing in said well, if desired.

in one presently preferred method of operation in accordance with the invention, an oxygen-containing gas is introduced into formation 12 through well or well 16 and a first combustion front is initiated in formation 12 at said production well 16. Said combustion front can be initiated in any conventionalmanner known to the art such as by igniting formation 12 with a downhole heater, by spontaneous ignition after air injection is started, or by other suitable method. Said oxygen-containing gas, such as air, can be initially introduced through conduit 14 or conduit 18 to support or maintain the combustion front. After said first combustion front has been well established, any injection of oxygen-containing gas through conduit 18 is terminated. Thereafter, said first combustion front is maintained by the introduction of oxygen-containing gas through conduit 14 and well 10. The injection of the oxygen-containing gas is continued at a rate and for a period of time sufficient to cause a said combustion front 22 to move out into said formation in a direction away from said production well 16 and towardsaid injection well 10 by counproduced from the formation via well 16 and conduit 20 in known manner. a

After said first combustion front 22 has moved out into the formation a substantial distance, such as indicated in FIG. 2, a

second combustion 'front is initiated in formation 12 by intentionally igniting said formation at the injection well 10. Said second combustion front is here shown at 24 after it has moved cm into the formation by direct drive. Since the oxygen-containing gas being introduced via conduit 14in well 10 must pass said second'com bustion front 24, essentially all of the oxygen is consumed in said front 24 and said first combustion front 22 is permitted to die out from lack of oxygen, During this direct drive portion of the process, hydrocarbons in the formation are driven through the formation and into and through the hot region B of the formation which has been traversed by said first combustion front 22, now inactive as shown in H6. 2. Hydrocarbons are recovered from the formation via production well 16 and conduit means 20.

As indicated above, one of the disadvantages of countercurrent drive in situ combustion processes is that uncontrolled autoignition nearly always occurs, sooner or later, in the formation'upstrea'm from the advancing front. Passage of the oxygen-containing gas through the formation to the countercurrent combustion front co causes a slow auto-oxidation of the oil or other hydrocarbons in said formation, with resultant heating of the oil until, finally, autoignition of said oil takes place. This heating of the formation and the oil therein could be valuable if controlled and utilized in a direct drive process to prevent buildup of liquid hydrocarbons downstream from the combustion front. It is a feature of the present invention that a direct drive in situ combustion is deliberately started and the countercurrent in situ combustion portion of the process is terminated before autoignition occurs, and in time to utilize the heat stored in the formation by the slow auto-oxidation of hydrocarbons during the countercurrent drive process.

The rate of auto-oxidation or autoheating in the formation in the region A between the injection well 10 and the countercurrent combustion front 22 is affected by the character of the oil in the formation, the initial ambient temperature of the formation, the rate of injection of the oxygen-containing gas, the oxygen content of said injected gas, and the reservoir or formation pressure. The first two of said items, i.e., character of the oil and fonnation temperature, are ordinarily known or readily available from core samples and/or reservoir logs. it has been found that the effect of the oxygen-containing gas injection rate is primarily one of'heat transfer, e.g., the flowing stream conducts heat through the formation away from a specific volume of the formation and increases the amount of oxygen carried to the combustion front. The oxygen content of the injected gases and the reservoir pressure can be corre- ,lated and expressed in terms of effective oxygen partial pressure. It has been found fromfield experience that one of the most important variables affecting the rate of auto-oxidation or autoheating is the oxygen partialpressure. An increase in oxygen partial pressure increases the rate of auto-oxidation. Thus, one knowing the character ofi the oil in the formation, the formation temperature, and the formation pressure, can calculate or determine the desirable injection rate and oxygen content or partial pressure for the injected oxygen-containing gases. Field experience has shown that one can estimate, and to' a large extent control, the time required for the oil in the formation to reach a temperature at which autoignition or spontaneous ignition occurs. Generally speaking, it has been found that the oil in the formation can be heated to a temperature of up to about 600,'preferably not more than about 500 F., without causing spontaneous ignition. If one does not wish to rely on calculations for estimating the temperature of the formation in the region A, one can'monitor said temperature by means of a series of temperature observation wells located between well 10 and well 16.

Similarly, field experience has shown that the reservoir temperature in the region B traversed by the countercurrent combustion front can be controlled to -a large extent by varying varying the oxygen concentration or partial pressure in the stream of oxygen-containing gases being supplied to the countercurrent combustion front. Thus, in the practice of the first stage of the invention process, it is desirable to balance (a) the gas injection rateand the oxygen partial pressure with (b) the necessity for supplying sufficient oxygen to maintain the countercurrent combustion front. For example, it is desirable that the oxygen-containing gases be injected at a rate and an-oxygen partial pressure which is sufficient to maintain the countercurrent combustion front but which is insufficient to heat the formation hydrocarbons in the region A between the injection well and the countercurrent combustion front to the point of early or premature autoignition.

In the practice of the invention the injection rates and the oxygen concentration or partial pressure for the oxygen-containing gases can be varied widely to accomplish the above objectives of the invention, depending upon formation pressure, formation porosity, and formation temperature. Generally speaking, the injection rate for said gases will be within the range of from about 50 to about 2000 s.c.f./hr./ft. of formation. It is preferredthat said oxygen-containing gases be injected at a rate within the range of from about 150 to about 500 s.c.f./hr./ft. of formation. However, any rates conventionally used in in situ combustion processes can be employed, depending upon formation conditions such as porosity, etc.

Air is the oxygen-containing gas most commonly employed in the practice of the invention. However, it is within the scope of the invention to employ air enriched with oxygen, or air diluted with flue gases or other essentially inert gases. It is also within the scope of. the invention to employ percent oxygen where economically available. Generally speaking, the oxygen-containing gases employed in the practice of the invention will contain from about 5 to about 50, preferably from about 15 to about 30 percent oxygen.

Said oxygen-containing gases can be injected at any pressure ranging from sufficient to inject the gas into the formation to just below the pressure where uncontrolled fracturing vention is not limited to any particular range of well spacing. Any spacing pattern can be employed'in which the process of the invention can be carried out. It is-desirable that the well spacing not be so great that the region of the formation between the injection well and the countercurrent combustion front (after said front has moved out into the formation an appreciable distance) cannot all be significantly heated before autoignition or spontaneous ignition occurs. Thus, the invention finds its greatest applicability when the injection well and the production well are spaced relatively close together.

Spacings within the range of from about 50 to about 600 feet, 7

preferably about 50 to about 300 feet, have'been found particularly useful. However, it is within the scope of the invention to employ well spacings outside said ranges.

As indicated above, it is desirable that the-first stage countercurrent in situ combustion continue long enough to accomplish significant heating by auto-oxidation of the region of the formation between the injection well and'saidcountercurrent combustion front. Depending upon the well spacing and the characteristics of the formation, this will usually have been accomplished when from about to about :75, preferably at least about 25 percent of the distance between the wells has been traversed by the countercurrent combustion front.

The following illustrative embodiment will serve to further illustrate the invention. A porous oil-bearing formation containing a heavy viscous crude oil having a gravity of about 8 API is penetrated by an injection well and a'production well, similarly as in FIGS. 1 and 2, and spaced about 300 feet apart. The ambient temperature of the formation is-aboutv 140 F. The formation pressure is about 1500 p.s.i.g. Air at the rate of 100 M.c.f./day/ft. of exposed formation isstarted into the formation through the production well and the formation ignited to establish a first combustion front within the formation.

After said first combustion front has been'established, injection of air through said production well iste'rminated. lnjec tion of air through the injection well is then started to establish a countercurrent drive for said first combustion front. Said countercurrent drive is carried out fora period of about 6 weeks. During this time said first combustion front travels 25 direct drive combustion front and the termination of the countercurrent drive front. I

Said direct drive combustion is continueduntil the formation between said injection well and said production well is burned out. During this direct drive stage of the process viscous oil is driven into the hot region of the formation previ-. ously traversed by the countercurrent combustion front. This results in the production of an upgraded crude oil having a reduced viscosity and increased gravity. Also, due to the previous heating of the formation region A between the two wells, there is no plugging of the formation by liquid hydrocarbons ahead of or downstream from thefdirect drive combustion front. 7

From the above disclosure of the invention it is evident that a number of advantages are realized in the practice of the invention. included among said advantages are: the elimination or control of the problem of autoignition' or spontaneous ignition during the countercurrent in situ combustion portion of the process; the elimination of the problem of liquid hydrocarbons blocking the formation downstream from the direct drive combustion front; the production of an upgraded crude oil during the major portion of the direct drive portion of the process as well as during the countercurrent drive portion of the process; and an overall increase in production due to heating of the formation. Still another advantage is that by intentionally starting the direct drive combustionprocess at the injection well before autoignitioir occurs out inthe formation, the problem of leaving unburned formation adjacent the in jection well, which can sometimes occur, is avoided.

While the invention has beendescribed and illustrated by employing one injection well and one production well, it will be understood that any number of injection wells and any number of production wells, arranged in any suitable pattern, can be employed in the practice of the invention.

While the invention has been described primarily with reference to recovering petroleum tars .and low gravity oils, the invention is likewise applicable to the recovery of higher gravity crude oils. The invention can, also be employed to recover oilfrom reservoirs which have alreadybeen subjected to primary and/or secondary recovery methods. The invention can also be employed in recovering Ihigh gravity oil from low energy reservoirs, e.g. reservoirs which contain very little, if any, dissolved gas, and thus have little, if any, reservoir pressure. t

While certain embodiments of the invention have been described for illustrative purposes, the invention is not limited thereto. Various other modifications of the invention will be apparent to those skilled in the art in view of this disclosure. Such modifications are within the spirit and scope of the dis closure.

I claim:

1. A process for producing hydrocarbons from a permeable oil-bearing subterranean formation penetrated by at least one injection well and at least one production well, which process comprises, in combination, the steps of:

a. injecting a stream of oxygen-containing gas through one of said wells into said formation;

b. initiating a first combustion front in said formation at said production well;

, c. terminating any injection of oxygen-containing gas through said production well; i

ygen-containing gas through said injection well at a rate and for a period of time sufficient to cause said first combustion front to move out into said formation in a direction away from said production well and toward said injection well by counterflow in situ combustion for a substantial distance, but insufficient for 'autoignition to occur in said formation between said injection well and said first comburstion front;

e. thereafter intentionally igniting a second combustion front in said formation at said injection well;

f. permitting said first combustion front to die out from lack of oxygen due to essentially all of the, oxygen in said oxygen-containing gas being consumed in said second combustion front;

g. continuing injection of said oxygen-containing gas through said injection well to move said second combustion front through said formation toward said production well by direct drive in situ combustion;

h. driving hydrocarbons in said formationthrough the area of said stratum traversed by said firsticombustion front and to said production well; and

'i. recovering hydrocarbon s from said production well.

2. A process according to claim ll wherein said formation contains a viscous oil. 4

3. A process according to claim 1 wherein said wells are spacedapart a distance within the range of from 50 to 600 feet.

4. A process according to claim 1 wherein hydrocarbons are produced from said formation during said step a.

5. A process according to claim 1 wherein saidoxygen-containing gas is injected during said step (d) at a rate within the range of from about 50 to about 2000 s.c.f./ hr./ft. of formation. Y

6. A process according to claim 5 wherein the injection rate of said oxygen-containing gas is within the range of from about to about 500 s. :.f./hr./ft. of formation.

maintaining said first combustion'front by injection of ox-' 8 about 600 F. but insufficient t'cause autoignition within said region. a

9. A process according to claim 8 wherein said oxygen-con- 'taining gas is air and is injected at a rate within the range of from about 50 to about 2000 s.c.f./hr./ft." of formation and said region of said formation is heated to a temperature of not more than 500 F. I 

